JPS61158420A - Hydraulic device for injection molding unit of plastic injection molding machine - Google Patents

Abstract

A hydraulic control system for the operation of three linear and one rotary hydraulic drive assemblies of the injection unit of an injection molding machine, comprising a variable delivery pump supplying drive fluid at a constant pressure gradient to several supply lines controlled by two control units which are arranged in parallel and feature proportional P/Q valves and pressure transducers, a smaller pressure maintenance pump which is controllable by a third proportional P/Q valve and switchable into one of the supply lines, and a hydraulic accumulator for the temporary supply of a large quantity of drive fluid. The proportional P/Q valves convert automatically from their flow rate programs, controlled by displacement-to-voltage converters on the injection unit, to pressure programs controlled by the pressure transducers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The invention relates to a regulating pump for supplying hydraulic oil to a hydraulic load of an injection molding unit via at least one load conduit, and a regulating pump provided in the load conduit. unit, this regulating unit has a proportional flow-pressure valve and a pressure sensor for pressure-related regulation, and a control return conduit attached to the regulating unit has a proportional The present invention relates to a hydraulic device for an injection molding unit of a plastic injection molding machine, which connects a load conduit after a flow at-pressure valve to a regulating mechanism of a regulating pump.

The operating pressure drop here means a pressure drop that is just sufficient as a basis for the operation and control of the regulating pump and is thus at the lower limit.

[Conventional technology]

A known hydraulic device of this type (German Patent No. 31 of the Federal Republic of Germany)
19095) maintains a minimum drive power compared to previous hydraulic systems based on a single proportional flow-pressure valve in the load conduit leading to multiple loads to accommodate different operating demands. It can be adjusted in various ways.

[Problem that the invention seeks to solve]

Starting from this, the ll! which forms the basis of the present invention! The problem is to develop hydraulic systems of the first type so that, in particular, the course of the injection process can be modified and accelerated by changes in the manufactured article to meet and accelerate some of the very different operating requirements. That's true.

[Means for solving problems]

To solve this problem, a second regulating unit is connected after the first regulating unit, with a proportional flow-pressure valve, a pressure sensor for pressure-related regulation (pressure program regulation) and a displacement-related Contains a displacement-to-voltage converter for regulation (flow program regulation).

〔Effect of the invention〕

Due to the functional cooperation of the first and second regulating units in the hydraulic system, the injection of plastic material into the mold and possibly also the loading and unloading of the injection molding unit from the mold is accelerated by simple additional measures. be able to.

This is done in the simplest case by programming the operating pressure drop via the pressure sensor of the first regulating unit. The operating pressure drop, which is thereby first set for energy saving, is determined by the proportional flow rate of the second regulating unit -
It serves as an auxiliary means to increase the switching speed of the pressure valve. This is because the delivery speed, which is increased by the high operating pressure drop, allows a small flow cross section in the second proportional flow-pressure valve and thus shortens the switching displacement. The high reaction speed of the proportional flow-pressure valve of the second regulating unit is particularly important in different courses of the injection process with multiple speed or pressure stages. The second regulating unit is therefore connected downstream of the first regulating unit with respect to its regulating operation, but not hydraulically.

[Immediate implementation]

The most effective means of speeding up the injection of plastic material are set out in claims 2 and 3. This allows the hydraulic reservoir to be refilled during injection and during the holding phase with an optimized operating pressure drop for the first adjustment unit.

A further and very simple measure for speeding up the injection of plastic material, which allows a more precise adjustment of the back pressure during preplasticization, is derived from patent claim 4. By connecting the cylinder space with the injection cylinder and the retraction cylinder, a differentially connected hydraulic system is created. This system significantly reduces the effective working surface. In the case of injection, this means a faster injection stroke of the feed screw. In the case of backpressure regulation, even higher backpressures occur in the proportional flow-pressure valve that regulates the backpressure. This means that the pressure adjustment scale for back pressure can be significantly increased. This allows the back pressure to be adjusted variably and precisely.

The possibility of adapting to different operating requirements is defined in claim 5.
It is derived from paragraphs 8 to 8.

〔Example〕

Two embodiments of the invention will be explained below with reference to the drawings.

The hydraulic device allows adjustment of the loading and unloading of the injection molding unit into the mold, as well as the pre-plasticization, the injection of plastic material into the mold and the retraction of the feed screw in the plasticizing cylinder. The retraction serves to reduce the pressure within the plasticizing cylinder before removing the injection molded unit from the mold. However, it is also possible to retreat the feed screw for disassembly or cleaning, etc.
often necessary. The hydraulic load of the injection molding unit is supplied with pressure oil via supply conduits from a regulating pump 2 with a relatively high delivery power and a regulating pump (pressure holding pump) 12 with a small delivery power. Intake filter I from tank 42
from the regulating pump 2 which sucks pressure oil through the pressure limiting valve 6.
A load line 3 with a flow rate leads to a first regulating unit El, which includes a proportional flow-pressure valve 4 and a pressure sensor 5 for pressure-related regulation (pressure program regulation). A control return line 43 provided in this first regulating unit El connects the load line 3 after the proportional flow-pressure valve 4 to the regulating mechanism 2a of the regulating pump 2 in order to maintain a constant operating pressure drop. There is.

The first adjustment unit E1 cooperates with a second adjustment unit E2 or E2' which is identical to this first adjustment unit El. A displacement-voltage converter 22 for displacement-related adjustment is attached to the second adjustment unit. In order to inject the plastic material, a first adjustment unit E1 and a second adjustment unit E2 are used.
If necessary, a hydraulic reservoir 29 with a pressure sensor 28 can be inserted between ' and the switching valve 27. A piston-cylinder unit (injection cylinder 24) that advances (injects plastic material) and retreats the feed screw 40.
and cylinder spaces 37 and 3 of the retraction cylinder 25)
8 can be connected by a switching valve 33. Adjustment unit E
After l, a second adjustment unit E2 or E2' is installed in the supply line 35 to the piston-cylinder unit (transfer cylinder) 23 for loading and unloading the injection molding unit and in the supply line 34 leading to the injection cylinder 24. A switching valve 15 is connected in a supply conduit 36 leading to the transfer cylinder 25. In the supply conduit 39 leading to the rotary oil motor 19 for the feed screw 40, a switching valve 1 is installed after the adjustment unit El.
6 is connected. A displacement cylinder 23 can be supplied via the switching valve 8 and the first regulating unit El by means of the pressure-maintaining pump 12.

During the injection of the plastics material and the subsequent pressure-holding phase during which the plastics material is pushed back into the mold, either by the regulating pump 2 via the regulating unit E1 or by the pressure-holding pump via the pressure connection valve 32 and the switching valve 27. Hydraulic reservoir 29 can be refilled selectively or simultaneously by regulating pump 2 and pressure-maintaining pump.

All speeds and pressures of the hydraulic system can be operated in a closed control loop with minimal energy consumption and negligible costs for hydraulic components.

The configuration of the control device will now be explained in detail in relation to the course of the injection cycle.

First Embodiment of Control During the Stage of Mounting and Detaching an Injection Molding Mold Position The regulating unit E2' with the proportional flow-pressure valve 9 and the pressure sensor 10 operates as a switching valve.

The speed and pressure are determined by a regulating unit El with a proportional flow-pressure valve 4 and a pressure capacitor 5. Due to the control return line 43, a constant operating pressure drop is maintained by this regulating unit El. In the case of velocity control W), feedback takes place via a displacement-to-voltage converter 21 which operates as a displacement sensor. By opening the proportional flow-pressure valve 4 of the adjustment unit El to a predetermined geometrical magnitude, the speed can also be controlled.The movement of the valve spool is detected by a displacement sensor and transferred as the actual value to the setpoint value. will be returned. If the pressure value specified in the program is reached during the movement, a transition to pressure regulation takes place. The actual pressure value is detected by a pressure sensor 5 and fed to an amplifier. When the programmed per-nozzle position is reached by the displacement-to-voltage converter 21 and the programmed per-nozzle pressure is reached simultaneously by 4 soil, 2 bags, 5 and 1O, the following occurs. In other words, the switching valve 8 connected upstream of the adjustment unit E2', which operates as a switching valve, is switched to the nozzle. The regulating pump 2 is thereby controlled to zero by the regulating unit E1. At the same time, the proportional flow rate to pressure valve 9 of the adjustment unit E2' operates as a pressure adjustment valve. The actual pressure value is detected by a pressure sensor lO and fed back to the inductor 1[i. This amplifier makes it possible to perform a setpoint-actual value comparison. Therefore displacement sensor 2
1, velocity feedback and displacement positioning take place.

2. Second embodiment of control in the mounting and dismounting stage of injection molds The speed adjustment, pressure adjustment and positioning are performed in the adjustment unit E2'.
This is done by means of a proportional flow-pressure valve 9. In this case, a regulating pump 2 and a pressure-maintaining pump 12 can also be used for supplying pressure oil. Therefore, when operating the regulating pump, parallel operation with other regulating pumps is possible. For speed regulation and positioning of the nozzle at the mold, the actual value is determined by the displacement-voltage converter 2.
1 returns it to the target value. For pressure regulation, the actual pressure value is detected by a pressure sensor lO and fed back. The control spool of the proportional flow-pressure valve 9 is configured in such a way that it is possible to position and stop the nozzle via the displacement sensor 21 without position adjustment, and the proportional flow-pressure valve 9 is closed. A pressure limiting valve 7 is inserted into a pressure conduit 47 leading from the pressure holding pump 12 to the regulating unit E2'.

3 Preplasticization (it amount) At this stage, the rotating feed screw 40 returns with the back pressure of the plastic material that accumulates in front of it. Feed screw 4
0 is driven by an oil motor 19 supplied via a supply conduit 39. This drive is effected via the switching valve 16 by the regulating unit E1. The required rotational speed of the feed screw 40 can be selectively adjusted or controlled via the proportional flow-pressure valve 4 of the regulating unit El. For rotation speed adjustment,
The pulses of the inductive proximity switch 20 are fed back to the amplifier as actual values. The rotational speed is controlled by opening the proportional flow-pressure valve 4 to a geometric size corresponding to the flow rate. The movement of the valve spool is then detected by a displacement sensor 4a and fed back as an actual value to the electronic amplifier. When a predetermined permissible maximum torque of the feed screw 40, which is measured as a pressure value by the pressure sensor 5, is reached, the actual pressure value is fed back. The rotation of the feed screw 40 is then effected by pressure regulation. Oil motor! 9 tank conduit 39a passes through the oil cooler 14 and the return filter injection molding unit.

The back pressure of the plastic material that builds up in front of the feed screw is
It is regulated via the proportional flow-pressure valve 18 of the regulating unit E2. The actual pressure value is then detected by pressure sensor 17 and fed back. Cylinder space 38 of retreat cylinder 25
is connected to the tank 42 by switching the switching valve 15 from position A to T, so that pressure oil can be supplied to the cylinder space 38 from the tank 42. The cylinder space 37 is depressurized via a tank line 41.

If extremely different or precise adjustments are required, the backpressure adjustment can also be carried out selectively in different ways. In this case, the backpressure is likewise regulated via a proportional flow-pressure valve 18, and the actual pressure value is detected by a pressure sensor 17 and fed back. However, in contrast to the backpressure regulation described above, the cylinder space 37 of the injection cylinder 25 is connected via a conduit to the cylinder space 38 of the retraction cylinder 25 by means of a switching valve 33 . This is because in the switching sequence, there is no need to supply pressure oil to the cylinder space 38 during plasticization.

By connecting the cylinder space 38 to the cylinder space 37, a differential connection is created, so that the effective area under pressure in the hydraulic system is significantly smaller. Therefore, the proportional flow rate −
A high pressure builds up in the pressure valve 8. This makes it possible to adjust the backpressure over a particularly large pressure adjustment scale, that is to say with great precision.

4 Injection of plastic material into the mold The injection speed and injection pressure are the proportional flow rate of the adjustment unit E2 -
It is regulated via a pressure valve 18.

The actual speed and position values of the feed screw 40 are fed back via a displacement-to-voltage converter 22, which acts as a displacement sensor. The actual pressure value is fed back by pressure sensor 17. The operating pressure drop, and thus the pressure drop from the regulating pump 2 to the pressure sensor 17, is freely selectable. The proportional flow-pressure valve 4 of the regulating unit E1 is then opened, making it possible to adjust the operating pressure drop via the control feedback line 43. In this respect, the adjustment unit El serves to adjust the optimal operating pressure drop during the withdrawal process and during the pressure retention phase.

For adjustment of the drawer, an injection cylinder 24 and an adjustment pump 2 are used.
Only a single proportional flow-pressure valve 18 operates between the two, thereby ensuring optimum energy utilization.

Since the adjustment unit E2 is installed in the plasticizing cylinder of the W direct injection molding unit, the supply conduit becomes extremely short.
This increases adjustment accuracy. During the injection process, the cylinder space 38 of the retracting cylinder 25 is connected to the tank 42 via the switching valve 15 .

If the injection speed is extremely high, injection can also be carried out in different ways. In other words, the cylinder space 38 of the retraction cylinder 25 is connected to the cylinder space 37 of the dispensing cylinder 25 via a conduit 45.44 by means of a switching valve 33.

The switching valve 15 is then in the shutoff position. Thus, with the same pump delivery power, a higher injection speed is obtained.

5 Retraction of the Feed Screw or Reduction of Back Pressure in the Plasticizing Cylinder Retraction of the feed screw 40 is initiated by switching the switching valve 15 in the supply conduit 35 from position P to A. The proportional flow-pressure valve 18 of the regulating unit E2 is then in the switching position A to T. Speed and pressure are in adjustment unit E
1 proportional flow-pressure valve 4, the speed of which can also be selectively controlled or adjusted. When a predetermined pressure value, measured via the pressure sensor 5, is reached, a pressure adjustment takes place.

6 Hydraulic reservoir injection of preplasticized plastics material If a very fast injection of plastics material is required, a hydraulic reservoir can be inserted into the supply line between the regulating units El and E2' via the switching valve 27. 29 is used. In this case, pressure oil is removed only from the hydraulic reservoir 29, which can be connected to the injection cylinder 24 via the pressure lines 34', 44 by means of the proportional flow pressure valve +8'. Filling of the hydraulic reservoir 29 is thereby possible during the injection process and during the pressure build-up phase. The hydraulic reservoir 29 is filled using the check valve 26 and the switching valve 2.
7 by the regulating pump 2, but optionally by the pressure holding pump 12, the switching valve 8' and the pressure connection valve 32.
It can also be done via. In the case of filling with regulating pump 2, the pressure drop to hydraulic reservoir 29 is freely selectable via pressure sensor 5. The filling pressure of the hydraulic reservoir, which is determined via the pressure sensor 28, can always be adapted to the specific consumption. Therefore, in any case
Only the amount of pressure oil required for the next injection process can be filled into the hydraulic reservoir 29. In order to adjust the required amount of oil, a pilot-controlled proportional flow-pressure valve +9a is provided in the adjustment unit E2'. This valve 19a is equipped with a displacement sensor 18b. The spring 18c ensures that the proportional flow-pressure valve 18 spools incorrectly. This spring 18c pushes the spool to the right to generate the necessary control oil pressure.

The hydraulic reservoir 29 is protected by a pressure limiting valve 31 and can be pressure relieved by a switching valve 30. The pressure line 34' of the hydraulic reservoir 29 passes through the switching valve 27 in any case.

The concept of proportional flow-pressure valves should be understood in a broad sense and includes servo valves.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of a hydraulic system of a hydraulic device, and FIG. 2 is a connection diagram of a hydraulic system having a hydraulic reservoir. 2... Adjustment pump, 3.34.35... Load conduit,
4, 18.18'...Proportional flow rate-pressure valve, 5, 17
... Pressure sensor, 21.22 ... Displacement-voltage converter, 23, 24 ... Load (piston-cylinder unit),
El, E2. E2'...Adjustment unit.

Claims (1)

Claims: 1. A regulating pump for supplying pressure oil to the hydraulic load of the injection molding unit via at least one load conduit, and a regulating unit provided in the load conduit, the regulating unit being proportional. With a flow-pressure valve and a pressure sensor for pressure-related regulation, a control return line attached to the regulating unit regulates the load line after the proportional flow-pressure valve in order to maintain a constant operating pressure drop. In those connected to the adjustment mechanism of the pump, the first
After the regulating unit (E1), a second regulating unit (E2, E2'') is connected, which includes a proportional flow-pressure valve (18, 18''), a pressure sensor (17) for pressure-related regulation, and Hydraulic device for an injection molding unit of a plastic injection molding machine, characterized in that it includes a displacement-voltage converter (22) for displacement-related regulation. 2 First adjustment unit (E1) and second adjustment unit (E2″
) between the hydraulic reservoir (29) and the pressure sensor (28).
2. Device according to claim 1, characterized in that the switch valve (27) is insertable by means of a switching valve (27). 3. The cylinder spaces (37, 38) of the piston-cylinder unit (24, 25) for advancing and retracting the feed screw flow rate of the injection molding machine are connectable to each other by a switching valve (33). Apparatus according to claim 1. 4 Piston-cylinder unit for attaching and detaching injection molding unit (2
3) in the supply conduit (35) and into the injection cylinder (2).
After the first regulating unit (E1), a second regulating unit (E2, E2″) is connected in the supply conduit (34) leading to the retracting cylinder (25) and in the supply conduit (1) leading to the retraction cylinder (25).
5. Device according to claim 1, characterized in that in 5) a switching valve (15) is connected after the first regulating unit (E1). 5 A patent characterized in that a switching valve (16) is connected after the first adjustment unit (E1) in the supply conduit (39) leading to the oil motor (19) for the feed screw (40). Apparatus according to claim 1. 6. The cylinder for mounting and dismounting the injection molding unit (23) can be supplied via the switching valve (8) and the second regulating unit (E2″) by an additional regulating pump (12) with a small delivery power. The device according to claim 4, characterized in that: 7. Attachment and detachment of the injection molding unit can be selectively adjusted by the first adjustment unit (E1) or the second adjustment unit (E2″). In the case of adjustment by the second adjustment unit (E2″),
The cylinder (23) for attaching and detaching the injection molding unit is connected to the adjustment pump (
2) or an additional regulating pump (12). 8 The hydraulic reservoir (29) is connected to the first regulating unit (E1) during the injection of the plastic material and during the subsequent pressure holding phase.
and can be selectively refilled by the regulating pump (2) via the switching valve (27) or by an additional regulating pump (12) via the pressure connection valve (32), or by the regulating pump (2) via the pressure connection valve (32). ) and an additional regulating pump (12).